NAME

FETCH - retrieve rows from a query using a cursor

SYNOPSIS

FETCH [ direction { FROM | IN } ] cursorname
where direction can be empty or one of:
NEXT
PRIOR
FIRST
LAST
ABSOLUTE count
RELATIVE countcount
ALL
FORWARD
FORWARD count
FORWARD ALL
BACKWARD
BACKWARD count
BACKWARD ALL

DESCRIPTION

FETCH retrieves rows using a previously-created cursor.
A cursor has an associated position, which is used by FETCH. The cursor
position can be before the first row of the query result, on any
particular row of the result, or after the last row of the result. When
created, a cursor is positioned before the first row. After fetching
some rows, the cursor is positioned on the row most recently retrieved.
If FETCH runs off the end of the available rows then the cursor is left
positioned after the last row, or before the first row if fetching
backward. FETCHALL or FETCHBACKWARDALL will always leave the cursor
positioned after the last row or before the first row.
The forms NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE fetch a single
row after moving the cursor appropriately. If there is no such row, an
empty result is returned, and the cursor is left positioned before the
first row or after the last row as appropriate.
The forms using FORWARD and BACKWARD retrieve the indicated number of
rows moving in the forward or backward direction, leaving the cursor
positioned on the last-returned row (or after/before all rows, if the
count exceeds the number of rows available).
RELATIVE 0, FORWARD 0, and BACKWARD 0 all request fetching the current
row without moving the cursor, that is, re-fetching the most recently
fetched row. This will succeed unless the cursor is positioned before
the first row or after the last row; in which case, no row is returned.

PARAMETERS

directiondirection defines the fetch direction and number of rows to
fetch. It can be one of the following:
NEXT Fetch the next row. This is the default if direction is
omitted.
PRIOR Fetch the prior row.
FIRST Fetch the first row of the query (same as ABSOLUTE 1).
LAST Fetch the last row of the query (same as ABSOLUTE -1).
ABSOLUTEcount
Fetch the count’th row of the query, or the abs(count)’th
row from the end if count is negative. Position before
first row or after last row if count is out of range; in
particular, ABSOLUTE 0 positions before the first row.
RELATIVEcount
Fetch the count’th succeeding row, or the abs(count)’th
prior row if count is negative. RELATIVE 0 re-fetches the
current row, if any.
count Fetch the next count rows (same as FORWARD count).
ALL Fetch all remaining rows (same as FORWARD ALL).
FORWARD
Fetch the next row (same as NEXT).
FORWARDcount
Fetch the next count rows. FORWARD 0 re-fetches the
current row.
FORWARDALL
Fetch all remaining rows.
BACKWARD
Fetch the prior row (same as PRIOR).
BACKWARDcount
Fetch the prior count rows (scanning backwards). BACKWARD
0 re-fetches the current row.
BACKWARDALL
Fetch all prior rows (scanning backwards).
countcount is a possibly-signed integer constant, determining the
location or number of rows to fetch. For FORWARD and BACKWARD
cases, specifying a negative count is equivalent to changing the
sense of FORWARD and BACKWARD.
cursorname
An open cursor’s name.

OUTPUTS

On successful completion, a FETCH command returns a command tag of the
form
FETCH count
The count is the number of rows fetched (possibly zero). Note that in
psql, the command tag will not actually be displayed, since psql
displays the fetched rows instead.

NOTES

The cursor should be declared with the SCROLL option if one intends to
use any variants of FETCH other than FETCHNEXT or FETCHFORWARD with a
positive count. For simple queries PostgreSQL will allow backwards
fetch from cursors not declared with SCROLL, but this behavior is best
not relied on. If the cursor is declared with NO SCROLL, no backward
fetches are allowed.
ABSOLUTE fetches are not any faster than navigating to the desired row
with a relative move: the underlying implementation must traverse all
the intermediate rows anyway. Negative absolute fetches are even
worse: the query must be read to the end to find the last row, and then
traversed backward from there. However, rewinding to the start of the
query (as with FETCH ABSOLUTE 0) is fast.
Updating data via a cursor is currently not supported by PostgreSQL.
DECLARE [declare(7)] is used to define a cursor. Use MOVE [move(7)] to
change cursor position without retrieving data.

COMPATIBILITY

The SQL standard defines FETCH for use in embedded SQL only. The
variant of FETCH described here returns the data as if it were a SELECT
result rather than placing it in host variables. Other than this point,
FETCH is fully upward-compatible with the SQL standard.
The FETCH forms involving FORWARD and BACKWARD, as well as the forms
FETCH count and FETCH ALL, in which FORWARD is implicit, are PostgreSQL
extensions.
The SQL standard allows only FROM preceding the cursor name; the option
to use IN is an extension.